How do I use for-each in Java?

By Wayan in Core API, Lang Package 0 Comment

Using for-each command to iterate arrays or a list can simplified our code. Below is an example how to do it in Java. The first loop is for iterating array and the second for iterating a list containing a some names.

package org.kodejava.lang;

import java.util.ArrayList;
import java.util.List;

public class ForEachExample {
    public static void main(String[] args) {
        Integer[] numbers = {10, 100, 1000, 10000, 100000, 1000000};

        for (Integer i : numbers) {
            System.out.println("Number: " + i);
        }

        List<String> names = new ArrayList<>();
        names.add("Musk");
        names.add("Nakamoto");
        names.add("Einstein");

        for (String name : names) {
            System.out.println("Name: " + name);
        }
    }
}

The result of the code snippet:

Number: 10
Number: 100
Number: 1000
Number: 10000
Number: 100000
Number: 1000000
Name: Musk
Name: Nakamoto
Name: Einstein

How do I convert string to an integer or number?

By Wayan in Core API, Lang Package 0 Comment 
package org.kodejava.lang;

public class StringToInteger {
    public static void main(String[] args) {
        // Some random selected number, could representing a decimal,
        // hexadecimal or octal number.
        String myLuckyNumber = "13";

        // We convert a string to an integer by invoking parseInt() method
        // of the Integer class.
        int number = Integer.parseInt(myLuckyNumber);
        System.out.println("My lucky number is: " + number);

        // We can also converting a string representation of a number other
        // then the decimal base, for instance an hexadecimal by providing
        // the radix to the method.
        number = Integer.parseInt(myLuckyNumber, 16);
        System.out.println("My lucky number is: " + number);

        number = Integer.parseInt(myLuckyNumber, 8);
        System.out.println("My lucky number is: " + number);
    }
}

Our code results are:

My lucky number is: 13
My lucky number is: 19
My lucky number is: 11

How do I create a zip file?

By Wayan in Zip and GZIP 0 Comment 
package org.kodejava.util.zip;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;

public class ZippingFileExample {
    public static void main(String[] args) {
        String source = "data.txt";
        String target = "data.zip";

        try (ZipOutputStream zos = 
                 new ZipOutputStream(new FileOutputStream(target));
             InputStream is = 
                 ZippingFileExample.class.getResourceAsStream("/" + source)) {
            if (is != null) {
                // Put a new ZipEntry in the ZipOutputStream
                zos.putNextEntry(new ZipEntry(source));

                int size;
                byte[] buffer = new byte[1024];

                // Read data to the end of the source file and write it
                // to the zip output stream.
                while ((size = is.read(buffer, 0, buffer.length)) > 0) {
                    zos.write(buffer, 0, size);
                }

                zos.closeEntry();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I get all table names from a database?

By Wayan in JDBC 0 Comment 
package org.kodejava.jdbc;

import java.sql.*;

public class GettingTableListExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // Gets the metadata of the database
            DatabaseMetaData metaData = connection.getMetaData();
            String[] types = {"TABLE"};

            ResultSet rs = metaData.getTables("kodejava", "kodejava", "%", types);
            while (rs.next()) {
                String tableCatalog = rs.getString(1);
                String tableSchema = rs.getString(2);
                String tableName = rs.getString(3);

                System.out.printf("%s - %s - %s%n",
                        tableCatalog, tableSchema, tableName);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Here is the result:

kodejava - null - author
kodejava - null - book_author
kodejava - null - book

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

Maven Central

How do I drop table from a database?

By Wayan in JDBC 0 Comment

This example is to show you how to delete or drop a table from your database. Basically we just send a DROP TABLE command and specify the table name to be deleted to the database. The example below show you how to do it in MySQL database.

package org.kodejava.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class DropTableExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // To delete a table from database we use the DROP TABLE
            // command and specify the table name to be dropped
            String sql = "DROP TABLE IF EXISTS book";

            // Create a statement
            Statement statement = connection.createStatement();
            // Execute the statement to delete the table
            statement.execute(sql);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

Maven Central